Diffusor

ABSTRACT

The guide device for the diffusor at the compressor impeller outlet of a radial compressor has guide blades with stepped inlet edges. The step is implemented by setting back the hub-side inlet edge. This meridional stepping divides the guide blades into two component blades, of which the first component blade is made longer than the second component blade. The set-back of the inlet edge of the hub-side component blade and the associated superposition of the noise fields which are produced on the front and rear inlet edge of the diffusor leads to improvement of the acoustic properties of the compressor.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to EP Application06405234.3 filed in Europe on May 26, 2006, the entire contents of whichare hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The disclosure relates to the field of compressors of exhaust gasturbochargers for supercharged internal combustion engines. It relatesto a guide device for the diffusor on the compressor impeller outlet ofa radial compressor and a compressor with this guide device.

BACKGROUND INFORMATION

In modern exhaust gas turbochargers, to increase the intake pressure ofinternal combustion engines, single-stage radial compressors with bladeddiffusors at the compressor impeller outlet are generally used. Thediffusors have a guide device with guide blades with prismatic,generally aerodynamic profiles. The outflow of the compressor impelleris hallmarked essentially by a so-called jet wake flow in which radiallylow-momentum flow collects on the side of the inlet housing (shroudside), while on the hub side there is a healthy flow. Thus the radialvelocity component of the flow drops over the height of the diffusorchannel.

In the design of compressor stages a compromise must always be foundbetween the aerodynamic performance, mechanical load and acoustic noiseformation by a compressor. Compressor stages with high specificabsorption capacity have long moving blades with natural vibration formswhich occur at relatively low frequencies and which are very easilyexcited and caused to oscillate. The main source of these excitations isa nonuniform pressure potential field which is produced by the guideblades of the guide device of the diffusor. According to experience, thecompressor stages with high specific absorption capacities also producehigh noise levels at the compressor outlet which are caused essentiallyby the impact of the flow fluctuations over time on the guide blades ofthe guide device of the diffusor.

One focus of continuing research for improving the stage consists indesigning radial compressors such that the pump limit is shifted to flowrates as small as possible without in doing so having to tolerateadverse effects on efficiency. If the characteristic diagrams arenarrow, numerous specifications with different blade heights and/ordiffusors for matching to the varied application must be observed; thisleads to high storage costs.

To reduce blade vibrations the moving blades of the compressor impellercan be thickened or the distance of the guide device of the diffusor tothe compressor impeller outlet can be increased to reduce excitation.The increase of the distance of the guide device of the diffusor leadsat the same time to a noise reduction. But both measures lead to areduction in efficiency, for which reason the desired thermodynamicperformance would be missed.

In order to correspond to the described flow lamination, guide bladestilted meridionally can be used in the guide device of the diffusors.This results in that faulty incident flow on the guide blade incidenceedges is minimized and thus better efficiency is achieved. In addition,the meridionally tilted guide blades cause a reduction of the vibrationexcitation of the guide blades and reduced exit noise generation by theblade wheel/guide wheel interaction. When using meridionally tiltedguide blades in the guide device of the diffusors at high absorptioncapacities strict acoustic requirements cannot be met under certaincircumstances. Production of diffusors with meridionally tilted guideblades is moreover much more complex than that of prismatic blades.Instead of being able to cut a blade in one cutting process, the profilemust be shaved over the height in several steps.

U.S. Pat. No. 5,178,516 discloses a guide device on the compressorimpeller outlet of radial compressors in which to improve flowproperties the inlet edges of the guide blades on the inlet side arenearer the compressor impeller outlet than on the hub side. With theinlet-side lengthening of the guide blades, the result should be that norecirculation flows occur locally directly radially outside thecompressor impeller outlet. Here it is explicitly stipulated that themaximum distance of the blade inlet edge on the entry side should beless than 10 out of one hundred of the outside radius of the compressormoving blades. The set-back inlet edge on the hub side is accordinglyspaced more than 10 out of one hundred of the outside radius of thecompressor moving blades away from the compressor impeller outlet. Theheight of the lengthened blade tip is stipulated at 10 to 60 out of onehundred of the height of the diffusor channel.

U.S. Pat. No. 5,529,457 discloses from a similar arrangement that forsimpler production different inlet edges of the guide blades can beimplemented by one stage.

With the lengthening of the guide blade tips which was proposed in thesetwo documents the attempt is made to enlarge the operating region of thecompressor. Noise abatement measures play no part in the details. Due tothe reduction of the distance of the inlet edges of the guide bladesfrom the compressor impeller outlet, with the suggested stepping of theinlet edge of the guide blades the noise at the compressor outlet andexcitation of blade vibrations however should rather increase.

SUMMARY

Noise abatement measures are disclosed for a compressor with highabsorption capacity. For example, a guide device is disclosed for thediffusor at the compressor impeller outlet of a radial compressor, inwhich the guide blades have meridionally stepped inlet edges, the stepbeing implemented by setting back the hub-side inlet edge. Thismeridional stepping divides the guide blades into two component blades,of which the first component blade is made longer than the secondcomponent blade.

The set-back of the inlet edge of the hub-side component blade and theassociated superposition of the noise fields which are produced on thefront and rear inlet edges of the guide blades of the diffusor leads toadditional improvement of the already favorable acoustic properties ofthe diffusors with meridionally tilted guide blades.

With the stepped diffusor a greater useful characteristic diagram widthat the same efficiency and lower exit noise can be achieved than for ameridionally tilted diffusor.

The thermodynamic performance is likewise improved by a diffusor withmeridionally stepped guide blades. While the radially low-momentum flowon the inlet side is guided by the long part of the profile such thatthe flow assumes the desired direction, on the lift side for a healthyflow (high in radial pulses) a very short diffusor with a large,extremely narrow cross section is used. It is known of diffusors withshort guide blades without a meridional tilt or step that they improvethe stability of the compressor stage and achieve good efficienciessince the flow-wetted area is small and thus friction losses are low.The improved stability of the flow leads to wider characteristicdiagrams. Thus, with one specification a greater bandwidth of engineoperating lines which differ in absorption behavior can be accommodated.In this way the number of required specifications is minimized and thusthe storage costs can be reduced.

Moreover, compared to the meridionally tilted guide blades, for theguide blades made stepped with component blades of varied length thereare advantages in production. In this case advantageously first of allthe guide blade profile is produced as a prismatic profile and then asmaller, likewise prismatic profile is reworked out of the hub-side partat a constant height. This reduces the production cost compared to ameridionally tilted diffusor.

BRIEF DESCRIPTION OF DRAWINGS

Various exemplary embodiments of the guide device are described belowusing the drawings.

FIG. 1 shows a section through an exemplary diffusor at the outlet ofthe blade wheel of a radial compressor with a first exemplary embodimentof the guide device having shortened component guide blades,

FIG. 2 shows a section through a diffusor at the outlet of a radialcompressor with a second exemplary embodiment of the guide device,

FIG. 3 shows a curve diagram with noise development as a function of theratio between the distances of the inlet edges of the component guideblades on the outlet edge of the moving blades of the compressorimpeller for different heights of the component guide blades, and

FIG. 4 shows a three-dimensional representation of the different curvebehaviors of the diagram as shown in FIG. 3.

DETAILED DESCRIPTION

In a compressor housing which is shown only partially in FIG. 1, acompressor impeller is arranged to be able to turn around an axis A. Thecompressor housing is schematically comprised of an inlet side housingpart 41 and a hub-side housing part 42. The compressor impeller sits ona shaft which for an exhaust gas turbocharger is driven by a turbinewhich is not shown. The compressor impeller surrounds the hub 32 and,located on the hub, a host of guide blades 31. They extend from theincident flow-side end of the compressor impeller as far as theoutflow-side end on the radial outside edge of the compressor impeller.The flow direction is indicated with a thick arrow.

In the flow direction farther downstream of the outflow-side end of thecompressor impeller, there is a diffusor. The diffusor is comprised ofthe diffusor walls and a guide device with several guide blades locateddistributed along the periphery. The diffusor walls border the flowchannel downstream of the compressor impeller.

The guide blades of the exemplary guide device are comprised of severalcomponent blades. In the first exemplary embodiment there are twocomponent blades 10 and 20. The first component blade 10 adjoins theinlet-side housing wall and extends into the interior of the diffusorchannel. The inlet edge 11 of the first component blade lies on a radiusr₁ which advantageously measures roughly 110 to 125 out of one hundredof the outer radius r of the outflow edges 33 of the guide blades 31 ofthe compressor impeller. An overly small distance can lead to vibrationproblems, while an overly large distance adversely affects theefficiency.

The inlet edge 21 of the second component blade is set back meridionallyrelative to the inlet edge of the first component blade. Considerationsleading to the disclosure and noise computations based thereon haveshown that the blade profile length l₂ of the second component blade 20with respect to the blade profile length l₁ of the first component blade10, or the ratio of the distances of the inlet edges of the componentblades from the outside radius of the outflow edges of the moving blades(r₂−r)/(r₁−r) can be optimized depending on the ratio of heights of thecomponent blades. The diagram in FIG. 3 shows the noise behavior for adifferent configuration of the stepped guide blades. Each curve showsthe noise behavior for the indicated ratio of the height of the firstcomponent blade to the total of the heights of all component blades h₁/has a function of the ratio of the distances of the inlet edges of thecomponent blades on the outside radius of the outflow edges of themoving blades (r₁−r)/(r₂−r).

Computations have shown that the noise can be reduced for a height ofthe first component blade h₁ of roughly 30 to 70 out of one hundred ofthe sum of the heights of all component blades h in the region of thedistance of the inlet edge of the first component blades from theoutside radius of the outflow edges of the moving blades (r₁−r) ofroughly 50 to 85 out of one hundred of the distance of the inlet edge ofthe second component blades from the outside radius of the outflow edgesof the guide blades (r₂−r).

The computed absolute minimum of noise development is at the height ofthe first component blade h₁ of roughly 38 to 42 (the value used for thecomputation was 40) out of one hundred of the sum of the heights of allcomponent blades h in the region of the distance of the inlet edge ofthe first component blades from the outside radius of the outflow edgesof the moving blades (r₁−r) of roughly 55 to 60 out of one hundred ofthe distance of the inlet edge of the second component blades from theoutside radius of the outflow edges of the guide blades (r₂−r). It mustbe watched that when the compressor geometries change, for example for adifferent number of blades or different specific absorption capacity,these values should experience certain deviations. The optimum regionshould thus lie around the aforementioned values depending on the exactgeometry of the compressor.

The computed values were experimentally confirmed.

The curve family of the diagram from FIG. 3 is shown again in FIG. 4three-dimensionally. Curves with constant noise values can be projectedonto the bottom area. Here it is shown again that the optimum is in theabove described region.

FIG. 2 shows a second exemplary embodiment of the guide device. Betweenthe first component blade 10 and the shortened second component blade 20there is a third component blade 25. This third component blade has ablade profile length which is between the blade profile lengths of thefirst and second component blades. Other stages can be implemented byother component blades. The guide blades acquire finer meridionalstepping by additional component blades, with which the guide device canbe altogether better matched to the flow structure along the height ofthe diffusor channel.

The first and second component blades and possible other componentblades have a common exit edge in one exemplary embodiment. It runstransversely over the entire height of the diffusor channel.

The moving blades of the guide device have aerodynamic, straight orcurved blade profiles.

In one exemplary embodiment, the blade profiles of the shorter componentblade at the time run entirely around the periphery within the bladeprofile of the next larger component blade.

In another exemplary embodiment, the blade profile of one shortercomponent blade at the time corresponds to the blade profile of onelonger component blade at the time scaled with a reduction factor lessthan 1.

In the production of the divided guide blades, in a first working stepthe guide blade is produced with the height of the diffusor channel.This guide blade already has the blade profile of the first componentblade on the inlet side. Then the shorter component blades are cut outof the blade profile of the original guide blade. In repeating passesthus several component blades can be produced, one shorter one out ofthe guide profile of the next larger. In this connection production isfacilitated by the blade inlet edges being made stepped.

The inlet edges of the two component blades of the guide device, whichedges are arranged stepped meridionally, lead to weakening of thepressure pulsation which is produced by the flow at the outlet of thecompressor impeller. This weakening of the pressure pulsation in turnhas a beneficial effect on the excitation of the vibration of the movingblades of the compressor impeller; this has a positive effect especiallywhen the moving blade thickness is reduced since in this way loading ofthe guide blades can be clearly reduced. On the other hand, thisweakening of the pressure pulsation and the associated, less strongexcitation allow a higher volumetric flow with the dimensions of thecompressor and diffusor remaining the same. The higher volumetric flowdue to the meridionally stepped inlet edges of the guide blades of thediffusor does not lead to an unallowable increase in the excitation ofthe moving blades of the compressor impeller.

It will be appreciated by those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. The presently disclosedembodiments are therefore considered in all respects to be illustrativeand not restricted. The scope of the invention is indicated by theappended claims rather than the foregoing description and all changesthat come within the meaning and range and equivalence thereof areintended to be embraced therein.

REFERENCE NUMBER LIST

-   10 first component blade (inlet side)-   11 inlet edge of the first component blade-   20 second component blade (hub side)-   21 inlet edge of the second component blade-   25 third component blade-   31 moving blades of the compressor impeller-   32 hub of compressor impeller-   33 outflow edge of the moving blades of the compressor impeller-   41 inlet-side housing-   42 hub-side housing-   l₁ blade profile length of the first component blade-   l₂ blade profile length of the second component blade-   h₁ blade height of the first component blade-   h total height of the first and second component blades-   r outside radius of the compressor impeller on the outflow edge of    the moving blades-   r₁ inside radius of the inlet edge of the first component blade-   r₂ inside radius of the inlet edge of the second component blade

1. Guide device for a diffusor on a compressor impeller outlet of aradial compressor, comprising: a plurality of guide blades, the guideblades being located between an inlet-side housing part and a hub-sidehousing part, each guide blade being divided into, a first, inlet-sidecomponent blade; and at least one second, hub-side component blade,wherein a blade profile length of the first component blade being largerthan a blade profile length of the second component blade, the firstcomponent blade having a height from 30 to 70 percent of a sum ofheights of all component blades along a blade inlet edge, and a distancefrom a blade inlet edge of the first component blade to an outsideradius of outflow edges of moving blades is 50 to 85 percent of adistance from an inlet edge of the second component blades to theoutside radius of the outflow edges of the moving blades, so that inoperation of the guide device in a radial compressor, a first part of anoutflow of the compressor impeller can be routed over the firstcomponent blade and a second part of the outflow which flows with astronger radial component is routed over the second component bladewhich has a set back blade inlet edge relative to the blade inlet of thefirst component blade.
 2. Guide device as claimed in claim 1, whereinthe first component blade on the blade inlet edge has an inside diameterwhich is 110 to 125 percent of an outer diameter of a compressorimpeller radius.
 3. Guide device as claimed in claim 1, wherein betweenthe first component blade and the second component blade there is atleast one third component blade, the third component blade extendingover a length which is between the blade profile length of the firstcomponent blade and the blade profile length of the second componentblade.
 4. Guide device for the diffusor of a radial compressor asclaimed in claim 1, wherein outflow edges of the component bladesjointly form a continuous outflow edge of the guide blades.
 5. Guidedevice for the diffusor of a radial compressor as claimed in claim 1,wherein a blade profile of the second component blade lies completelywithin a blade profile of the first component blade.
 6. Guide device forthe diffusor of a radial compressor as claimed in claim 1, wherein ablade profile of one second component blade corresponds to a bladeprofile of one first component blade scaled with a reduction factor. 7.An exhaust gas turbocharger, comprising: a guide device for a diffusoron a compressor impeller outlet of a radial compressor, including: aplurality of guide blades, the guide blades being located between aninlet-side housing part and a hub-side housing part, each guide bladebeing divided into, a first, inlet-side component blade; and at leastone second, hub-side component blade, wherein a blade profile length ofthe first component blade being larger than a blade profile length ofthe second component blade, the first component blade having a heightfrom 30 to 70 percent of a sum of heights of all component blades alonga blade inlet edge, and a distance from a blade inlet edge of the firstcomponent blade to an outside radius of outflow edges of moving bladesis 50 to 85 percent of a distance from an inlet edge of the secondcomponent blades to the outside radius of the outflow edges of themoving blades, so that in operation of the guide device in a radialcompressor, a first part of an outflow of the compressor impeller can berouted over the first component blade and a second part of the outflowwhich flows with a stronger radial component is routed over the secondcomponent blade which has a set back blade inlet edge relative to theblade inlet of the first component blade.
 8. Guide device for thediffusor of a radial compressor as claimed in claim 3, wherein outflowedges of the component blades jointly form a continuous outflow edge ofthe guide blades.
 9. Guide device for the diffusor of a radialcompressor as claimed in claim 3, wherein a blade profile of the secondcomponent blade lies completely within a blade profile of the firstcomponent blade.
 10. Guide device for the diffusor of a radialcompressor as claimed in claim 3, wherein a blade profile of one secondcomponent blade corresponds to a blade profile of one first componentblade scaled with a reduction factor.
 11. The exhaust gas turbocharger,as claimed in claim 7, wherein a blade profile of one second componentblade corresponds to a blade profile of one first component blade scaledwith a reduction factor.